检索结果-南通市图书馆

Storage capacity model for cloud download

在线全文

学校读者我要写书评

暂无评论

The Journal of China Universities of Posts and Telecommunications 2012年第5期19卷 83-91页

作者： xu Ying-ying AO nai-xiang CHEN Chang-jia School of Electronics and Information Engineering Beijing Jiaotong UniversityBeijing 100044China

With the rise and world wide deployment of cloud utilities, the principle of the cloud download is proposed to provide high-quality file content distribution by using dedicated servers as cloud cache to guarantee the data availability and enhance the data transfer rate. As the system scales up to a large population, how to design appropriate storage capacity of cloud cache is a key challenge for cloud download. In this paper, primary elements impacting on storage capacity are explored through deliberating in large-scale commercial cloud download system, i.e. general user usage pattern and available period. And based on statistical analysis of real-world traces, we formulate storage capacity related to these two elements, which is the original contribution different from all previous works. This model gives guidance of potential system policy design. Finally, the effectivity of this model is demonstrated by simulation results compared with empirical data of practical system.

关键词： cloud download storage capacity model available period usage pattern

Evaluation Method and Probabilistic Index of Voltage Sag Severity Considering Point-on-wave

在线全文

学校读者我要写书评

暂无评论

Journal of Modern Power Systems and Clean Energy 2021年第3期9卷 633-638页

作者： Guopei Wu Qing zhong Qizhang He zhong xu Guangzhou Power Supply Bureau Cooperation GuangzhouChina the School of Electric Power South China University of TechnologyGuangzhouChina

The impact of voltage sag on sensitive devices is related to the time when the sag ***,the point-on-wave of a sag is ***,this paper presents a nov-el approach to evaluate the voltage sag severity considering a random ***,the uncertainty of equipment malfunction is ***,under a given residual voltage,the relationship between the point-on-wave and the duration that the device can withstand is described with a fitting ***,a voltage sag probabilistic index is proposed to describe the *** evaluation procedure is also ***,three types of releasers are tested and analyzed to determine the effectiveness of the proposed *** evaluation method can help instruct electrical engineers establish more well-grounded sag mitigation proposals.

关键词： Voltage sag evaluation method severity index probabilistic index

Effect of inorganic salt on the thermal degradation of nitrocellulose and reaction mechanism of its mixture

在线全文

学校读者我要写书评

暂无评论

Defence Technology（防务技术） 2023年第9期27卷 111-118页

作者： Guo-zhong xu xu Gao Mi Li zhong-xuan Han Lin Jiang School of Mechanical Engineering Nanjing University of Science and TechnologyChina

In this study,to better understand the reaction mechanism between inorganic salts and nitrocellulose,CaCO_(3) and Li_(2)CO_(3) were evaluated with respect to their effects on the thermal degradation of NC in nitrogen atmosphere using TG/DSC at three different heating rates(2,5,10 K/min).The numerical relationship between activation energy(E)and conversion rate was obtained by FWO and KAS method,and it was discovered that CaCO_(3) could improve the thermal stability of *** energy values were calculated by Kissinger method,and it was found that NC that contain Li2CO3had the highest activation energy while NC containing CaCO3had the lowest E *** combining the thermal analysis data with Malek method,the most probable mechanism model of thermal degradation is obtained as Sesták-Berggren model,which expression is f(α)=α^(m)(1-α)^(n).As a result of this study,there are certain guiding principles that can be applied to the pyrolysis reaction model and to the actual production process of nitrocellulose.

关键词： Thermal analysis Thermal decomposition mechanism Malek method Nitrocellulose Inorganic salt

HNCO： a molecule that traces low-velocity shocks

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2018年第2期18卷 19-36页

作者： nai-Ping Yu Jing-Long xu Jun-Jie Wang National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China NAOC-TU Joint Center for Astrophysics Lhasa 850000 China

Using data from Millimetre Astronomy Legacy Team Survey at 90 GHz （MALT90）, we present a molecular line study of a sample of APEX Telescope Large Area Survey of the Galaxy （ATLASGAL） clumps. Twelve emission lines have been detected in all. We found that in most sources, emissions of HC3N, HN13C, CH3CN, HNCO and SiO show more compact distributions than those of HCO＋, HNC, HCN and N2H＋. By comparing with other molecular lines, we found that the abun- dance of HNCO （x（HNCO）） correlates well with other species such as HC3N, HNC, C2H, H13CO＋ and N2H＋. Previous studies indicate the HNCO abundance could be enhanced by shocks. However, in this study, we find the abundance of HNCO does not correlate well with that of SiO, which is also a good tracer of shocks. We suggest this may be because HNCO and SiO trace different parts of shocks. Our analysis indicates that the velocity of a shock traced by HNCO tends to be lower than that traced by SiO. In the low-velocity shocks traced by HNCO, the HNCO abundance increases faster than that of SiO. While in the relatively high-velocity shocks traced by SiO, the SiO abundance increases faster than that of HNCO. We suggest that in the infrared dark cloud MSXDC G331.71＋00.59, high-velocity shocks are destroying the molecule HNCO.

关键词： stars: formation- ISM: abundances- ISM: clouds- ISM: molecules

Experimental Study of Hydrodynamic and Self-Buried Behavior of Submarine Pipeline with Perpendicular Spoilers

在线全文

学校读者我要写书评

暂无评论

China Ocean Engineering 2021年第2期35卷 250-261页

作者： FAN Hong-xia WANG Jian-zhong ZHU Li-jun WANG nai-ru CHEN Huai State Key Laboratory of Hydrology Water Resources and Hydraulic EngineeringNanjing Hydraulic Research InstituteNanjing 210029China

The spoiler is a kind of device to disturb current and promote *** present,all submarine pipeline spoilers at home and abroad are parallel spoilers,that is,the plane of the spoiler is parallel to the vertical plane of the pipeline *** to the results of indoor experiments,when the pipeline with the forward spoiler is installed perpendicular to the direction of water flow,the spoiler will accelerate the seabed erosion and cause the pipeline to endure downward pressure,which will eventually cause the pipeline self-buried to form a ***,when the pipeline direction is consistent with the flow direction,the self-buried behavior and protective effect is *** aiming at the defect that the forward spoiler cannot be self-buried when the direction of the pipeline and the flow are basically parallel,the spoiler burying aid device perpendicular to the pipeline axis has been innovatively developed,and the hydrodynamic changes and sediment erosion characteristics near the pipeline after the installation of the device were studied based on the *** reveal that although the perpendicular spoiler cannot generate downforce,it can greatly increase the turbulent kinetic energy of the flow and the rate of sediment *** larger the angle between the pipeline axis and the spoiler plane is,the larger the increase in turbulent energy will *** increase in turbulent energy near the bed surface can reach up about 70%when the angle is 90°,while serious sediment erosion mainly occurs along both sides of the pipeline with a distance of about 2−4 times the pipe *** the future,we can further explore the influence of the perpendicular spoiler size and installation position on the pipeline downforce and the effect of burying *** the same time,field tests on the perpendicular spoiler burying aid device currently developed will conduct to observe the actual effect of perpendicular spoiler promoting pipeline scouring and buryi

关键词： submarine pipeline spoiler self-burial turbulent kinetic energy sediment erosion

Valency Study of Vanadium in Stone Coal of Southern China

在线全文

学校读者我要写书评

暂无评论

Rare Metals 1990年第2期10卷 110-116页

作者： xu, Guozhen Ge, nai'e Chen, Jianping Shen, Shaobo Chinese Univ of Geosciences China

Vanadium - bearing stone coal is a new resource of vanadium. V in stone coal mainly exists in three oxidation states: 7.84% V(III), 72.08% V(IV) and 20.08% V(V). The change and distribution of valency during oxidizing roasting shows that organic matter in the coal determines the valency at low temperatures. At about 450°C, V(III) is completely oxidized to V(IV); above 500°C, temperature is the most important factor for the oxidation of V. At 700-1000°C, 92% of V in the coal has been oxidized to V(V). At higher temperature, no more oxidation of V takes place, equilibrium being established. The role of NaCl in the recovery of V2O5 from the coal is discussed. The best conditions for roasting are an oxidation-chlorination atmosphere, temperature 800°C for 30 minutes, ore:NaCl = 100:10, ηroast reaching 90%.

关键词： Coal Deposits Peoples Republic of China Mineral Industry and Resources Peoples Republic of China

Microstructure and tensile properties of A356 alloy with different Sc/Zr additions

在线全文

学校读者我要写书评

暂无评论

Rare Metals 2021年第9期40卷 2514-2522页

作者： Shou-Peng xu Chun-Sheng Shi nai-Qin Zhao Chun-Nian He School of Materials Science and Engineering and Tianjin Key Laboratory of Composites and Functional Materials Tianjin UniversityTianjin 300350China Collaborative Innovation Center of Chemical Science and Engineering Tianjin 300072China

Addition of rare earth elements for improving the tensile properties of aluminum alloys has attracted great attention. In this study, a systematic analysis on the microstructure and tensile properties of A356–0.13 Ti alloys with different contents of scandium(Sc) and scandium/zirconium(Sc/Zr) after solution and aging treatment process was carried out. The addition of Sc/Zr into A356–0.13 Ti alloys can greatly refine the grain size and modify the deleterious coarse eutectic Si structure and harmful acicular iron-containing phase morphology. As a result, the maximum value of strength(298 MPa) and ductility(elongation of 8.4%) are acquired by co-addition of Sc/Zr after solution and aging treatment process, which indicates that the tensile properties of A356 alloy are greatly enhanced by the synergistic effect of co-addition of Sc/Zr.

关键词： Aluminum alloys Sc/Zr Tensile properties Solution and aging treatment

Novel model of material removal rate on ultrasonic-assisted chemical mechanical polishing for sapphire

在线全文

学校读者我要写书评

暂无评论

Friction 2023年第11期11卷 2073-2090页

作者： Mufang ZHOU Min zhong Wenhu xu Department of Mechanical Engineering Key Laboratory of TribologyNanchang UniversityNanchang 330031China

Ultrasonic-assisted chemical mechanical polishing(UA-CMP)can greatly improve the sapphire material removal and surface quality,but its polishing mechanism is still *** paper proposed a novel model of material removal rate(MRR)to explore the mechanism of sapphire *** contains two modes,namely two-body wear and ***,the atomic force microscopy(AFM)in-situ study,computational fluid dynamics(CFD)simulation,and polishing experiments were conducted to verify the model and reveal the polishing *** the AFM in-situ studies,the tip scratched the reaction layer on the sapphire *** pit with a 0.22 nm depth is the evidence of two-body *** CFD simulation showed that abrasives could be driven by the ultrasonic vibration to impact the sapphire surface at high *** maximum total velocity and the air volume fraction(AVF)in the central area increased from 0.26 to 0.55 m/s and 20%to 49%,respectively,with the rising amplitudes of 1–3μ***,the maximum total velocity rose slightly from 0.33 to 0.42 m/s,and the AVF was nearly unchanged under 40–80 r/*** indicated that the ultrasonic energy has great effects on the abrasive-impact *** UA-CMP experimental results exhibited that there was 63.7%improvement in MRR when the polishing velocities rose from 40 to 80 r/*** roughness of the polished sapphire surface was R_(a)=0.07 *** identified that the higher speed achieved greater MRR mainly through the two-body wear *** study is beneficial to further understanding the UA-CMP mechanism and promoting the development of UA-CMP technology.

关键词： sapphire ultrasonic-assisted chemical mechanical polishing(UA-CMP) material removal rate(MRR)predictive model atomic force microscopy(AFM)in-situ studies computational fluid dynamics(CFD)

A review on food oral tribology

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Friction 2022年第12期10卷 1927-1966页

作者： Wenhu xu Shuaike YU Min zhong School of Mechatronics Engineering Key Laboratory of TribologyNanchang UniversityNanchang 330031China

Food entering the oral cavity undergoes a series of complex processing *** is subjected to compression and shearing by the teeth,tongue,and palate to reduce its size and mix with saliva until it is *** oral processing behaviors are thought to be closely related to both food and oral frictional *** effort has been made in recent decades about food oral tribology to explore this complicated lubrication *** the lubrication mechanism of food in the mouth is important for improving the consumption experience and developing the novel *** paper provides a new perspective on the effects of composition,texture,structure,and saliva-food component interactions on lubrication properties of different foods,the relationship between sensory perception and oral frictional behavior,and the mechanism and pattern of lubrication categorized by common food *** roles of tribology in the improvement of food taste,the search for healthier ingredient substitutes,functional foods,and the development of green foods are *** and numerical prediction models among physical properties,sensory perception,and frictional behavior of food are *** of simulating oral processing,such as the selection of friction pair materials,physical modification of contact surfaces,addition of saliva,different modes of motion,and contact forms are concluded and *** progress of commercial friction apparatus as well as customized friction devices applied to the food sector in recent years are *** characteristics,performances,and applications of these tribological instruments are analyzed and *** addition,the results achieved by oral tribology in identifying adulterated foods and ensuring food safety are ***,some suggestions are put forward for the current challenges and future development of food oral tribology.

关键词： food oral tribology in vitro friction tests lubrication behavior Stribeck curve sensory perception food development and detection